Endodontics or root canal therapy is that branch of dentistry that deals with the diseases of the dental pulp and associated tissues. One aspect of endodontics comprises the treatment of infected root canals, the removal of diseased pulp tissues, followed by the biomechanical modification and the subsequent filling of the pulp canal (root canal). Root canal therapy is generally indicated for teeth having sound external structures but having diseased, dead or dying pulp tissues. Such teeth may or may not generally possess intact enamel and dentin and are satisfactorily engaged with bony tissue. In such teeth, the pulp tissue and excised portions of the root should be replaced by a biocompatible substitute.
One technique for the preparation of a root canal involves creating a coronal access opening with a conventional dental drill. A tool is used for gross removal of pulp material from the root canal through the coronal access opening. The void formed is enlarged with reamers and/or files to result in a fully excavated cavity. Debris is removed from this cavity by flushing and the cavity is cleansed to remove all diseased tissue. Following chemical antisepsis, the excavated canal is ready for filling.
A basic method involves inserting a filling cone into a root canal and cementing therein to obturate the canal. Lateral condensation is a method in which several filling cones, a primary cone and auxiliary cones, are inserted into a root canal. The primary cone is inserted and cemented to the seat of the root canal. Using a tapered spreader, the primary cone is then squeezed against the side of the root canal and a second cone is inserted and cemented into place. This process is continued until the root canal is completely obturated which can require up to 10 to 15 filling cones. Vertical condensation of warm or hot gutta percha is yet another method of sealing root canals. After cementing a primary cone short of the apex of the root canal, heat application is alternated with a series of smaller and smaller pluggers until the gutta percha is moved to the apex. This is often possible when the smallest plugger approaches the apex of the tooth within 3 to 5 millimeters. The space is then backfilled. Lateral canals are packed and sealed as a consequence of lateral expansion of a wave of heated gutta percha. Alternatively, small segments of gutta percha can be used in this method that are inserted into the root canal, heated in order they can adhere to one another and each backfilled one at a time until the root canal is filled. All three of these methods, the single filling cone, lateral condensation and vertical condensation apply root canal cement or sealer around the individual cones or in between segments as a binding agent.
Another method employs an injection gun that injects warm or hot gutta percha filling material into a root canal. The injector initially places heated gutta percha at the seat of the root canal which is then condensed with a plugger into the root tip. The injector then backfills the root canal by injecting additional gutta percha into the root canal until it is obturated. A similar method involves heating gutta percha on a flexible metal carrier used to insert the gutta percha into the root canal. The carrier may be a solid rod, or a hollow rod, situated in the center of a master cone. The rod is connected to a handle which may be removed by slipping it out of the hollow rod, or cutting it off if it is a solid rod. While these systems provide for convenient and quick obturation of the canal, they pose a removal problem for the dentist who has to place a post.
Of all the methods used for obturating a canal, there is no device currently available that will allow a doctor to simultaneously obturate a root canal and place an endodontic post. Currently, an endodontist will perform the root canal procedure and the obturation during one patient visit. After the canal is obturated and temporarily sealed, the patient is frequently treated by a second dentist who will place the post. To do so, the gutta percha has to be removed from the canal until only a portion 5 mm or so from the apex remains to act as an apical seal. The rods inside the current systems make gutta percha removal much more difficult since the coronal portion of the gutta percha rod has to be removed to allow for the placement of the endodontic post. One way to overcome this problem has been to notch the obturating rod with a bur. Then, when the obturator is placed in the canal it is twisted, snapping off the apical portion. The longer coronal portion is removed. It is then re-introduced into the canal and the gutta percha is stripped off by means of pulling the rod through an endodontic stop. Since the endodontic stop is extremely narrow, the gutta percha is pulled from the rod as it is withdrawn and the gutta percha remains in the canal. It is subsequently condensed. As a result of this technique, the restoring dentist does not have to deal with the rod and only has to remove the gutta percha to make room for the post. Some gutta percha may remain on the walls of the canal jeopardizing the bond strength of the post the radicular dentin. Reinfection of the treated tooth can be a problem because the endodontist performing the root canal procedure will seal the coronal opening with a temporary stopping agent which can leak oral fluids carrying bacterial into the canal opening.
It is desirable to reduce the steps and time involved in performing obturation and placement of a post in a root canal. It would be beneficial to limit the obturation and post placement to a single visit to the dentist or prosthodontist. It is advantageous to reduce and/or eliminate the leakage problems associated with poor sealing at the coronal end of the canal.